Latex, Silicone or Butyl? Matching Caulk to the Joint

Tom Silva, a general contractor, says you cannot caulk over a failed joint: new silicone "will look good for about an hour," but it will not stick. That rule frames his walk-through of caulk types with host Kevin O'Connor, who notes the aisle offers "an endless selection."

Latex for interior joints

A painter will use latex caulk on interior walls, Silva says. It goes around casing, trim and baseboard, wherever a wall meets a transition such as a molding. Latex fills the gap and is paintable. He likes primer on the wall before caulking because it gives the caulk more adhesion.

Acrylic with silicone outside

For exterior gaps or holes that will be painted, Silva would go to an acrylic caulk with silicone added. The acrylic brings adhesion capability, and the silicone adds water protection that plain latex would not give. Exterior caulk sees more expansion and contraction, so it needs to flow and move with the joint.

100% silicone for wet areas

Silva only likes 100% silicone. It is pricey and comes in many colors because it cannot really be painted. He recommends it where a shower wall meets the tub, since that joint must stick well and be waterproof so water does not get behind the wall.

Butyl for metal and movement

For connecting two pieces of metal, such as on gutters, Silva points to butyl. He says it is used a lot in the commercial industry and should be used more. It is a rubber sealant that stays soft for a long time, though it can be messy. He also uses it for a long expansion joint in a tile floor: instead of grout, he caulks it in a color matching the grout. Butyl adheres to the tile and bends and stretches as the floor expands and contracts.

Prep and application

To redo a failed joint, the old material has to come off completely. Around a tub, Silva scrapes it clean with a razor blade, then rubs it with a cleaner. Sometimes he uses lacquer thinner or denatured alcohol. The joint must be dry before a new coat goes on.

The small hole on a caulk gun has a cutter: pull the trigger, put the tube tip in the hole, and it cuts the tip off. Some people pull the bead and some push it. Silva always pulls. He controls flow by easing off the trigger, and pushing drives caulk into a crack.